<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var age;
        age = prompt('输入年龄');
        alert(age);
    </script>

</head>

<body>

</body>

</html>